The present invention is directed to compositions and methods of lowering the incidence of fouling of marine and aquatic animals, particularly shellfish, and apparatus used in aquaculture.
Shellfish aquaculture, in dollar terms, represents well over half of the Australian aquaculture industry, with pearl oysters and Sydney rock oysters the most important sectors. Total Australian market value in 1994-5 was $302 million (worldwide, an estimated $6.8 billion). As with other sectors of the aquaculture industry, biofoulingxe2x80x94settlement and growth of unwanted marine organismsxe2x80x94comprises a significant cost to the industry. Unlike finfish culture, however, where fouling is a problem only for gear (ropes, pens, trays, etc.), fouling in shellfish culture is also a significant problem for the animals themselves. This is because the shells of oysters, mussels, scallops etc. are surfaces for settlement of fouling organisms.
Fouling of shellfish reduces their growth, survival, and marketability. The costs of fouling to the shellfish industry in Australia and worldwide are substantial. It has been estimated that the decline in production of Sydney rock oysters in the Port Stephens (NSW Australia) estuary from xcx9c$20 million p.a. to $5 million p.a. over the past 10 years was due almost entirely to xe2x80x9covercatchxe2x80x9d (fouling) of Pacific oysters on the shells of the cultured Sydney rock oysters, which renders them unmarketable. Moreover, the true costs of biofouling are often underestimated. For example, if biofouling could be prevented on rock oysters, they could be grown subtidally rather than intertidally. Growth would consequently be enhanced, and time to market significantly reduced. Such advantages are not usually included in costs associated with biofouling.
Currently fouling on shellfish is controlled in several ways. One way is manual cleaning, which is very inefficient and costly. For example, it is common practice for pearl oyster farmers in northern Australia to remove and clean each oyster on a farm every 7-14 days. The cost of this practice for the sector is between $8 and $20 million p.a., which represents 3-7%) of the total market value of pearls in Australia. Other methods of controlling biofouling are frequent and prolonged emersion, or even dipping briefly in near boiling water (both methods are used for Sydney rock oysters).
Current methods of controlling biofouling are clearly inefficient, costly and time consuming. The present inventors have developed a method for treating shellfish which inhibits fouling for at least 10 weeks and which has no adverse effect on survival of the treated shellfish. This is the first antifouling coating designed for application to living shellfish.
In a first aspect, the present invention consists in an antifouling coating composition when used for application to cultured marine or aquatic shellfish or aquaculture apparatus, the composition comprising a substantially non-toxic carrier selected from the group consisting of shellac, latex, casein, wax, and polymers which form hydrogels and an antifouling agent belonging to the families of isothiazolones or furanones, wherein the composition, when applied to a shellfish, is substantially non-toxic to the shellfish and reduces or prevents fouling of the shellfish.
The antifouling composition according to the present invention is considered as being non-toxic if it can be applied to the shellfish without adversely effecting the growth or survival of that shellfish during the period in which the shellfish is exposed to the composition applied thereto. The shellfish is preferably a scallop, abalone, mussel, clam, pearl oyster, or edible oyster. The furanones may be natural or modified furanones produced by marine algae or synthetically produced furanones or mixtures thereof. A mixture of synthetic furanones found to be particularly suitable is called herein 2/8/1, where
2 is (5Z)-3-butyl-4-bromo-5-(bromomethylidene)-2(5H)-furanone;
8 is 3-butyl-5-(dibromomethylidene)-2(5H)-furanone; and
1 is 3-butyl-4-bromo-5-(dibromomethylidene)-2(5H)-furanone.
The substantially non-toxic carrier can be natural, synthetic or a combination of both. It will be appreciated that the carrier should be able to stick or attach to the surface of shellfish and the like and remain substantially attached in an aqueous environment for a reasonable period of time. The carrier should also be miscible with the antifouling agent without adversely affecting the antifouling action of the agent. Natural carriers suitable include polymers which form hydrogels like Phytagel or preferably derived from shellac, a resinous excretion of the insect Laccifer (Tachardia) lacca Kerr, order Homoptera, family Coccidae (xe2x80x9clacxe2x80x9d beetle secretions). Other suitable carriers include but not limited to latex or casein gel. The carrier should be substantially non-toxic to the shellfish to which the coating is applied.
Examples of suitable isothiazolones and furanones are shown in FIG. 1. Preferably, the isothiazolone antifouling agent is (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one; FIG. 1) produced and sold by Rohm and Haas under the name Sea-Nine 211(trademark).
In a preferred embodiment of the first aspect of the present invention, the antifouling agents are used at a concentration of about 1 to 40%, more preferably from about 4 to 20% (w/w) of coating. In particular, a concentration of 15% has been found to be particularly effective when used with dried xe2x80x9clacxe2x80x9d beetle secretions dissolved in ethanol (from about 10 to 50% on a weight:volume basis). It will be appreciated that mixtures of antifouling agents (natural, synthetic, or commercial) may also be used to prepare the coating according to the present invention. The coating may further include other ingredients in the form of plasticisers, preservatives, solvents, organic additives and diluents, and water.
In a second aspect, the present invention consists in a method of reducing or inhibiting fouling of a cultured marine or aquatic shellfish, the method comprising treating at least part of the surface of the shellfish with an antifouling coating composition comprising a carrier and an antifouling agent belonging to the family of isothiazolones or furanones, wherein the carrier and the antifouling agent are substantially non-toxic to the shellfish.
The shellfish is preferably a scallop, abalone, pearl, mussel, clam, oyster, or edible oyster. The coating may be applied to the shellfish by any suitable means. Examples include painting, spraying, electrostatic spraying, brushing, and dipping.
In a third aspect, the present invention consists in the use of an antifouling composition according to the first aspect of the present invention to reduce or inhibit the fouling of a marine or aquatic shellfish.
In a fourth aspect, the present invention consists in method of reducing or inhibiting the fouling of an aquaculture apparatus, the method comprising treating at least part of the surface of the aquaculture apparatus with an antifouling coating composition according to the first aspect of the present invention.
The aquaculture apparatus suitable for treatment may be any apparatus used in mariculture and aquaculture industries. Examples include netting, mesh, panels, trays, ropes, floats, pumps, and monitoring equipment. The coating may be applied to the apparatus by any suitable means. Examples include painting, spraying, electrostatic spraying, brushing, and dipping.
The advantage of this aspect of the present invention is that the composition used adds significantly less weight to the treated apparatus and is not toxic to marine and aquatic animals in use. Traditional use of conventional antifouling compositions which include heavy metals for example have been found to be unsatisfactory due to the weight added to the apparatus as well as being potentially toxic to the marine organisms grown in the particular aquaculture.
In a fifth aspect, the present invention consists in the use of an antifouling composition according to the first aspect of the present invention to reduce or inhibit the fouling of aquaculture apparatus.
Throughout this specification, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, or variations such as xe2x80x9ccomprisesxe2x80x9d or xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.